This invention relates to a hood suitable for a steel processing vessel and, more particularly, to a vessel utilizing argon-oxygen decarburization.
The first commercial heat utilizing argon-oxygen decarburization was produced in 1967. However, by the end of 1977, just ten years later, approximately 75-80% of the United States stainless steel production was made using this process. The process essentially is the decarburization of metal through the use of oxygen with argon or some other inert gas. The refining process is carried out in vessels similar to converters by blowing the oxygen-inert gas mixture into the molten bath through submerged tuyeres located in the lower sides of the vessel. The process is based upon thermodynamic equation for the oxidation of carbon in the presence of chromium: EQU Cr.sub.3 O.sub.4 + 4C + 3Cr + 4 CO(g)
This formula shows that for any given temperature, the partial pressure of CO must be reduced in order to maximize the Cr to C ratio. Lowering the partial pressure of CO can be done by mixing a gas that is preferable inert with the CO.
However, in addition to the carbon monoxide which is given off in the AOD process, substantial quantities of oxides such as those of iron, chromium and nickle evolve from the decarburization vessel. These metallic fumes are dense and therefore potentially injurious. Therefore it is imperative that some means such as a hood be provided to collect the fumes.
However, the problem was not solved simply by providing an enclosure with an exhaust fan because the argon-oxygen refining vessel had to be replaced from time-to-time because of the degeneration of the refractory lining and the vessel also adapted a number of different attitudes depending on the character of the operation, viz., blowing, charging, sampling, tapping, etc.
I have discovered that a two-part hood, one part being fixed while the other is movable and with the movable part being equipped with a draft damper in one face, has solved the problem of providing a means for maximum control of the metallurgical fumes while utilizing minimum quantities of air that have to be moved.
Further details and advantages of the invention may be seen in the ensuing specification.